This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This proposal is part of our ongoing structural studies aimed at the characterization of the multi-domain human Estrogen Receptor (hER), its interaction with regulator/effector proteins and potential therapeutic small molecules. In the past we have collected data at the APS on the first protein-protein interaction of the hER ligand binding domain (LBD), complexed with its monobody (pdb code: 2OCF) and also on complexes of LBD with various ligands (with Estetrol in the last run, pdb code: 3L03). We have obtained crystals of new ligand complexes with the LBD, as well as crystals of the other domains of hER. In addition, we have well-diffracting crystals of Menin, multiple endocrine neoplasia protein, that has been shown to form a complex with the hER. We request beam time to screen these crystals, evaluate them for diffraction quality and collect data on those that diffract well.